The Orica site on Kooragang Island in New South Wales manufactures ammonia and nitric acid which are then used to produce ammonium nitrate for the mining sector.
WSP was engaged to assist with two regulatory compliance requirements associated with legacy contamination issues at the site, which has been in operation since 1969. The project included designing and implementing a remediation system to mitigate migration of groundwater contaminated with arsenic. WSP also investigated the extent and nature of legacy nutrient contamination from historical operations at the facility.
Our team assessed the feasibility of remediation options for the arsenic contamination in soil and groundwater and prepared a remediation action plan that not only met the regulatory objectives but was also cost-effective and would minimise disruption to site operations. We assisted with gaining planning approval for implementation of the program. Our team then produced a detailed design of the selected cap and containment remediation system (cut-off wall) to effectively isolate arsenic containing soil and groundwater, and subsequently provided validation services throughout its construction.
The design of the arsenic remediation system enabled it to be constructed within the site constraints (close proximity to two boundaries) and without the requirement to key the base of the cell into a low permeable geological unit (typical for cap and containment systems) which enabled the depth of the system to be minimised. WSP then prepared Construction Quality Assurance reports for both the cut-off wall and cap, as well as the Validation report for the remediation program. Our work was reviewed by an Accredited Contaminated Land Site Auditor who prepared a Site Audit Report and Site Audit Statement confirming the works had been completed in accordance with regulatory requirements and the land was suitable for ongoing industrial land use.
To investigate the legacy nutrient contamination, we undertook a detailed assessment to delineate the presence of nutrients (predominantly ammonia and nitrate) across the whole site. The investigation included soil and groundwater on and off site, seepage water at the adjacent river foreshore, surface water, sediment, and sediment pore water in the river system down-gradient of the facility. We also undertook an ecological risk assessment including assessment of benthic infauna (aquatic creatures living in the sediments).
A key aspect of the project involved a study of the hyporheic zone using environmental tracers to understand the geochemical process occurring within the riverbed. This assessment verified the fate and transport of nutrients. In combination with the ecological risk assessment, this demonstrated that the risk to the ecology in the receiving river environment was low. The outcome of the investigations enables Orica to focus future work on source control activities.
For both the arsenic remediation and nutrient investigation programs, our sound scientific solutions achieved pragmatic outcomes and compliance with the regulatory requirements.
* This work was performed by Golder professionals who joined WSP in an acquisition completed in 2021.
